Self-release adhesives



3,034,909 SELF-RELEASE ADHESIVES Robert H. Sams, Aidan, and Claire H.Jeglurn, Swarthmore, Pa., assignors to Philadelphia Quartz Company,Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Filed Dec.11, 1958, Ser. No. 779,567 9 Claims. (Cl. 106-80) INTRODUCTION Thisinvention generally relates to a method for decreasing the adhesion ofsilicate adhesives to heated metallic surfaces. More particularly, thisinvention involves incorporating organicfiamylmphnsphatesin combinationwith other additives in silicate adhesives so as to decrease the metaladhering properties of the silicate adhesive.

THE PROBLEM In the production of a laminated paperboard the adhesive isapplied to the surface of one sheet and a second sheet is pressed overthe adhesive layer and held in the laminated position until the adhesivehas set primarily by loss of moisture. In the manufacture of corrugatedpaperboard for example, the adhesive is applied to the tips of thecorrugations and a liner sheet is applied in position in contact withthe flute tips of the corrugation. The adhesive is then dried by passingthe web over heated metal plates called platens in the case of thedoublebacker or a heated roll in the case of the single-face liner. Inthe practice of this process the laminated sheets may become misalignedand the adhesive on the fiute tips at the edge of the web may be scrapedoff onto the hot metal surfaces or if too heavy a glue spread is appliedsome may ooze from the edge of the combined sheet and drip onto the hotplaten. The adhesive may also come into contact with the hot metalsurfaces if a liner sheet breaks and the unprotected flute tips comeinto direct contact with the platen.

Soluble silicates readily attach themselves to metal surfaces. They arepolar adhesives and form a strong bond with the metal when dried out.Furthermore, the dry silicate adhesive itself is strong and hard andglassy. Ridges and rough spots formed by the dried adhesive will scratchthe outer surfaces of the laminated boards in passing over them. It istherefore necessary for the operator to remove the hard drippings andaccumulation first by chipping them off by hand and then by scraping andpolishing the metal surface to restore it to its original smoothcondition. This cleaning operation is slow and tedious and must beunderstaken 2 or 3 times a day in some cases depending on the ability ofthe operator to schedule board of increasingly narrow width and to avoidaccidents to the paper liner. Silicate adhesives nevertheless continueto be used by the corrugating industry particularly where board havingextra strength and rigidity is desired. Oil coatings on metal rollersand graphite coatings on metal aprons to reduce scraping have been ofsome assistance.

A solution to the silicate clean-up problem has been sought for overtwenty years. Generally, two approaches have been taken. One is toprovide a protective coating for the metal surfaces which may becomesmeared with silicate. However, a satisfactory coating must not only besilicate-resistant but must withstand temperatures up to 400 F. as wellas vigorous wear of the paper sheet passing over it continuously. Thesecond approach is to modify the adhesive itself with additives.However, a satisfactory additive must not only be an effective partingagent toward metal, but must be compatible with the silicate adhesive,add little to its cost or odor and not interfere with its intendedpurpose of gluing paper. Consideration has also been given to changingthe metal of which the corrugating equipment is constructed but even ifa satisfactory solution were found in this way, it would be difiicult tohave it accepted by the manufacturers of such equipment.

It has long been known that surface active agents may be added to sodiumsilicate solutions to increase the wetting property in variousindustrial uses. In general, surface active agents are of little benefitin increasing the ease of wetting by soluble silicate adhesives. Theyalso tend to increase the viscosity of the solution and are moreexpensive than the silicate while tending to reduce the tensile strengthof the bond to paper. It has also been known that 0.5% isoamylorthophosphate added to N sodium silicate will reduce the adhesion tometal but not sufiiciently to be practical.

We have investigated several hundred additives for their effect on theease of separation of the soluble silicate adhesives from the hot metalsurface. Prior to the discovery of this invention, the best material wehad found was the condensation product of a rosin ester with maleicanhydride. Maleic anhydride is an unsaturated organic compound with ahigh dipole moment. The condensate with rosin has the highest possibleratio of carboxyl groups per molecule. However, the melting point of thesodium salt is far above the temperature of the hot metal platen. Whilethe use of this material did receive some industrial acceptance, itadded to the cost of the adhesive and required at least a gentle tap toremove lumps from the hot surface.

A number of prior art patents have dealt with this problem, as forinstance, Nos. 2,347,419; 2,671,747; 2,736,678; 2,772,177; 2,788,285;and 2,834,744.

OBJECTS The main object of the present invention is to provide acomposition and method for decreasing the adhesion of an adhesivesilicate composition to heated metal surfaces generally. These and otherobjects will occur to those skilled in the art from the description ofthe invention set forth below.

THE INVENTION BROADLY We have discovered that by incorporating acombination of an isomer of an amyl ester of phosphoric acid with onechemical compound selected from the group of urea and sugar and/or onechemical compound selected from the group consisting of triethanolamineand Mersize (a trademarked product of the Monsanto Chemical Companycomprising a condensation product of rosin and maleic anhydride) with asilicate adhesive we can obtain a good corrugated board bond and yet anyadhesive which is spilled and dries on the heated plates of thecorrugator is more easily removed than any other silicate adhesivemodified in any other known manner.

THE SILICATE ADHESIVE We have found that any sodium silicate typeadhesive can be used in accordance with this invention. As is wellknown, aqueous sodium silicate alone forms highly satisfactory adhesivematerials. It is therefore contemplated that simple combinations ofaqueous sodium silicate, an organic amyl phosphate with urea or sugar ortriethanolamine or Mersize can be produced in accordance with thisinvention. Likewise, as is well known in the prior art, a considerablenumber of additive" compounds may be combined with aqueous sodiumsilicate in order to produce a useful modified silicate adhesive. Thisinvention contemplates incorporating organic amyl phosphates and atleast one from the suggested groups in these modi fied silicateadhesives in order to decrease the metal adhering properties of theadhesive. Specific examples of such modified silicate adhesives can befound in Patents Nos. 2,239,358; 2,554,035; 2,669,282; 2,772,996 and2,681,290.

Especially preferred silicate adhesives which may be used as a base inthis invention range in weight ratio of SiO: to Na O from about 2 to 4.These silicates may have from 35 to 45% solids content. They may becombined with up to 10% starch, up to 20% clay, up to 10% urea, up to 2%triethanolamine, up to 10% sugar, up to 2% Mersize and other materialscommonly added to silicate adhesives.

THE ORGANIC AMYL PHOSPHATES Specific examples of simple isomers of amylesters of phosphoric acid which are included within the scope of thisinvention are as follows:

(1) Amyl acid phosphate (2) Monodiamyl acid phosphate (3)Monodi-iso-amyl acid orthophosphate (4) Mono-iso-amyl acidorthophosphate It is prefeerred that the organic amyl phosphates beincorporated in the silicate adhesive in an amount ranging between 0.25and 2.0% of the silicate adhesive.

THE GROUP SUGAR AND UREA While it has been known that 5% or more of ureawill decrease resistance to separation of silicate adhesive from hotmetal, this decrease, as shown below, has not been sufficient forpractical use. Urea combined with other materials is more effective andwe have now found that when combined with an organic amyl phosphate,even less than 5% of urea will provide silicate adhesives which separateat practical resistance levels. We have found that for practicalpurposes ordinary cane sugar may be substituted for urea.

THE GROUP MERSIZE AND TRIETHANOL- AMINE While it has been known thataddition of from about 0.1 to 2% of triethanolamine or Mersize tosilicate adhesives will decrease resistance to separation from hotmetal, again, the decrease has not resulted in product acceptance and wenow find that when coupled with one of the organic amyl phosphates,there is a synergistic decrease in the resistance to separation.

Furthermore we find the very best results when we combine the organicamyl phosphate, the urea or sugar, and the triethanolamine or Mersize inone silicate adhe sive having the approximate range of 1 to 5% of ureaor cane sugar, 0.1 to 2% triethanolamine or Mersize, 0.2 to 2% oforganic amyl phosphate, 0 to 20% of clay, 0 to commercial starch and theremainder substantially soluble silicate solution having a ratio of SiO;to Na O of 2 to 4 at a concentration permitting machine applicationsatisfactory for the purpose in hand. The preferred range of organicamyl phosphate is 0.25 to 1%.

METHOD FOR TESTING DEGREE OF ADHESION TO METAL There are a number ofways in which the additives for a silicate adhesive may be tested.First, there is the visual comparison in which the adhesive mixture isallowed to dry on a surface heated to the ordinary platen or hot platetemperature of the corrugating machine. The dried silicate puffs up andthe blob or coating is chipped off manually. A blob of N silicate heatedin this manner would be so hard that a metal instrument is needed todrive off and scrape away the residual adhesive. A good self-releasingadhesive can be knocked loose with a piece of stiff cardboard or linerboard such as is used for manufacturing corrugated boxes and the residuerubbed away with the surface of a liner board. This manual testingmethod gives a rough comparison but it is difiicult to compare theprecise relative metal adhering values of materials in this manner.

A more precise testing procedure is described in an article entitledAdhesion of Sodium Silicate to Metal" by John H. Wills and Robert H.Sams, published in TAPPI. July 1950, page 83A. In this test procedure,the puffed silicate residue was formed on the hot plate and then theresistance to crushing or shear was obtained by forcing a blade throughthe honey-combed structure just above the interface between the metaland the dried film. This resistance is shown as Table I in the reprint.

A still better method of determinating the clean-up resistancequantitatively was developed in our laboratory. In this method a papercylinder 0.5 inch high having an ID. equal to that of a nickel (2.0 cm.)was placed upright on the hot plate surface. A piece of wire shaped toform a fiat coil with a loop rising above its center and having theoutside diameter of a penny (1.8 cm.) was rested on the hot plate withinthe paper cylinder or well. About /43 inch depth of adhesive was pouredinto the paper well. around and over the coil of wire. After theadhesive became thoroughly baked at the 350 F. temperature of the hotplate (20 minutes were allowed) the force in pounds required to lift thewire and its surrounding adhesive crust from the hot plate surface wasmeasured with a push-pull gauge. The wire loop was cleaned before reuse.With this method the following results were obtained:

Clean-up resistance (in lbs.) N sodium silicate 7.5 97 N sodiumsilicate, 1% Mersize, 2% urea 2.1

(N" sodium silicate has a gravity of 41 B. and a ratio of one part ofN320 to 3.22 parts of SiO Mersize" is a condensation product of rosinand maleic anhydride.)

In a series of tests in which a sugar was substituted for the urea, itwas found that while commercial sugar had considerable effect in aidingclean-up, it was somewhat less effective than urea. Also, whentriethanolamine was substituted for Mersize, the results were nearly asgood. It is more miscible with the silicate and foams less.

PRELIMINARY TREATMENT OF THE METAL The very best separation from a metalsurface has been produced using our special adhesive with a specificallyprepared silicone film on the surface of the metal as described inExample 4. Other surface coating materials have shown good separationbut have not been as resistant to wear.

Such other coatings which showed satisfactory release of hot silicateresidue and some appreciable resistance to wear were Teflon(polytetrafiuoroethylene) coverings and a waxy chromate. Also, mixturesof 1 part of organic phosphate and 2 parts of turpentine gavesatisfactory resistance to the silicate but unsatisfactory resistance towear. The same organic phosphates which were used as additives showedbetter than normal effectiveness as a coating material.

EXAMPLES The following examples are illustrative of some preferredembodiments in accordance with this invention. It should be understoodthat these examples are not intended to limit the invention and thatobvious changes may be made by those skilled in the art without changingthe essential characteristics or basic concepts of the invention. Theparts and percentages are by weight unless otherwise indicated.

Example 1 A 41 B. solution of sodium silicate (having a ratio of 1NaO:3.22SiO was prepared for use as an adhesive. When tested according tothe previously described wire hook procedure this material was found tohave a clean-up resistance of 7.5 lbs-9.5 lbs.

Example 2 When the sodium silicate adhesive of Example 1 was modified bythe addition of 0.5% mono-isoamyl acid orthophosphate (referred to asphosphate) and the resistance to removal of the dry film was compared,it was found that while the phosphate did increase the ease of removalof the silicate film, it was not as satisfactory as when Mersize wasused alone. Similarly, when 2% urea was used with the silicate adhesiveof Example 1 re moval of the dried film was no easier than with theMersize additive, but a mixture of 2% urea and 1% of Mersize ortriethanolamine in the silicate did improve the ease of removal. If cornsugar was used in place of urea the dry film was nearly as easy toremove.

When 1% of Mersize and 0.5% phosphate were added to the silicateadhesive there was considerable improvement over the prior mixtures andwhen a combination of 96.5% N, 1% Mersize CD-Z, 2% urea, and 0.5% ofphosphate was used, the dry cake came away quite cleanly at a very lighttouch and was decidedly easier to remove than the combination of 1%Mersize, 2% urea and 97% N" which required a removal force of 2 to 3.

Pull. 111s.

t l l l i t t l l about 1.5

Example 3 A first (#1) commercial silicate adhesive was prepared havingthe following composition:

752: of pearl starch 77.5 72 of "N" sodium silicate 8.5% of Bardenair-classified clay 7.0% of water A second (#2) modified commercialsilicate adhesive was made having the following composition:

0.5% monoiso-amyl acid orthophosphate 0.1% of NaOH 1.5% of industrialcrystal urea 0.5% of technical triethanolamine 75.0% of sodium silicate7.0% of pearl starch 8.5% of Harden air-classified clay 6.9% of waterFrontthe above it will be seen that 2.5% of the N sodium silicatecontent of adhesive #1 was replaced with 2.5% of four other ingredientsin order to produce #2. The viscosity of adhesive -."-.1 at 75 F. was53.4 Stormer seconds and the viscosity of adhesive #2 at 75 F. was 93.4.

in order to compare the relative adhesion of the above adhesives to hotmetal, a laboratory hot plate was used to heat a sheet of stainlesssteel 0.0833 inch thick. The sheet was cleaned by abrasion and thenadjusted so that the sheet temperature rose to a maximum of about 340 F.in about minutes. The previously described testing procedure with thewire hook was used. The strength required to lift the adhesive from thestainless steel sheet was 6.8 pounds for adhesive #1 but only 1.4 poundsfor adhesive #2.

Example 4 A further test was made using coatings of F-lZl siliconesolution silicone solids in VM 8: P Naphtha, reference 5-203, November1954). The coating solution contained 4 parts of F-l2l silicone fluid, 6parts of naphtha, 0.5 part of powdered aluminum (to increase thevisibility of the film), 2 parts of Catalyst XY-26 (lead 2-ethylhexoatesolution). The stainless steel sheet was first cleaned by abrasion andthen the Fl2l silicone coating solution was applied with a soft brush.After an hour of air-drying the coated steel sheet was placed on a warmhot plate to'heat the surface quickly to 340 F. A half hour after thewarming began, the coated area was rubbed 100 times with a piece ofKraft liner Then the lift resistance of adhesive #1 of Example 3 fromthe coated area was determined immediately. A short time later, the liftrequired by adhesive #2 of Example 3 was determined on an adjacent partof the coated area.

In this case the lift resistance of adhesive :1 was only 1.1 pounds. Theadhesive #2 was less than 0.1 pound. Actually. in some later cases itwas found that adhesive :2 separated voluntarily from the specialcoating.

Example 5 A standard formula was prepared which contained:

All of the ingredients except the silicate were combined to form aclear, thin solution and then the silicate was agitated vigorously whilethe solution was added to it. After the mixing foam had subsided theadhesives were tested for the regular Stormer viscosity at F. also forhot plate clean-up resistance in pounds and for the strength in poundsof B-flute bond specimens prepared with the adhesives and conditionedfor at least two days. The B-flute bond test was made with the standardThwing- Albert electro-hydraulic tensile tester flute bond measuringequipment.

In the following table variations of the standard formula are indicatedunder composition.

Composition 10017.Nsilit-a1e. .\'0 uruanitphosphate t- The amyl1011051)]! phosphate... Amy] acid phosp crea ed to acid phosphate, 0.5part of water, 0.2 part of NaOH plus 1.8 parts of water, 1.5 parts ofindustrial crystal urea, 0.5 part of technical triethanolamine, 94 partsof "N" sodium silicate and 1 part of Barden clay. This mixture had aviscosity of 45.5 Stormer seconds and a hot plate cleanup resistance of2.1.

Example 6 A further illustration of the advantage of employing asilicate adhesive containing an organic amyl phosphate was carried outon a full plant scale. Two additive concentrates (concentrate #3 andconcentrate #4) were pre- 7 pared ready for mixing with the regilarplant silicate adhesive.

Concentrate #3 consisted of:

396 parts of urea 66 parts of triethanolamine 396 parts of water 5142parts of N sodium silicate This mixture was prepared by first heatingthe 396 parts of water to ISO-160 F. The heat was then turned off andthe 396 parts of urea were added to the water. The water was agitatedduring this solution period until the urea was completely dissolved. Thesolution had a temperature of about 80 F. Then the 66 parts oftriethanolamine were added to the mixture with stirring until the liquidwas entirely clean and uniform. This solution was then mixed with 5142parts of N sodium silicate by adding the solution slowly in a smallstream while vigorously stirring the N sodium silicate with a Lightninmixer. Agitation was continued for 10 minutes after all of the mixturehad been added. The final solution was allowed to stand for an houruntil the foam had been en tirely dissipated.

Another concentrate, concentrate #4, was prepared USlnQI 90 parts ofurea 162 parts of water 6 parts of fiake caustic 30 parts oftriethanolamine 42 parts of amyl acid phosphate 5670 parts of N sodiumsilicate 162 parts of water at ordinary temperature was placed in amixing vessel and 42 parts of amyl acid phosphate was added withoutstirring. Then 6 parts of the fiake caustic was added while the solutionwas agitated and agitation was continued until the solution becameclear. Then 90 parts of the same crystal urea were added and thesolution agitated until all was dissolved. Following this, 30 parts ofthe triethanolamine was added and thorough- 1y mixed in. This mixturewas then added to 5670 parts of N sodium silicate in a larger mixingtank. The mixture was added slowly in a small stream to the sodiumsilicate in the vortex of the Lightnin mixer. and agitation wascontinued for 20 minutes after all of the solution had been added. Thefinal mixture was then allowed to stand for about an hour until the foamhad disappeared.

Concentrate #3 had a viscosity of 18.5 Stormer seconds while concentrate4 had a viscosity of 40.6 Stormer seconds. When the plant adhesive wassimulated using 88.3 parts of concentrate #3 and with 4.4 parts ofstarch and 7.3 parts of clay, the viscosity was 42.9 seconds and theclean-up force required was 2.0. With 83.2 parts of concentrate #4, 5.1parts of water, 4.4 parts of starch and 7.3 parts of clay, the viscositywas 38.7 Stormer seconds and the clean-up force required was 1.8 pounds.These mixtures were designed so that the final viscosity would be in therange of a normal viscosity and the cleanup value below about 2 pounds.A standard plant adhesive was made up with 83.2 parts of N" sodiumsilicate, 5.1 parts of water, 4.4 parts of starch and 7.3 parts of clay.This had a Stormer viscosity of 48.3 and a cleanup resistance of 9.5pounds. In these tests the starch was a Hoosier pearl starch and theclay was Barden clay.

When run on the regular corrugating machine. the actual adhesivecontaining concentrate #4 exhibited no difficulty with odor, mixing orfoaming or with corrugator operation or board quality. Clean-up aroundthe single-facer and double-backer was definitely easier than with theregular adhesive, although the residue did not pop olf without aid. Theviscosity of a sample was 41.6 Stormer seconds and clean-up resistancewas 0.2 lb.

When the plant adhesive containing concentrate #3 was used, some slightfoam was noted. Corrugator operation and board quality were satisfactoryand clean-up was easier than with regular adhesive. A sample had aviscosity of 30.3 seconds and the clean-up resistance was 2.3 pounds.This compares very favorably with the above figures of 48.3 seconds and9.5 pounds clean-up resistance for the regular silicate-clay-starchadhesive.

These tests were run with B-fiute. Kraft 42 pound liners and 26 poundbogus medium were combined at the corrugator speed of 290 to 300 f.p.m.The adhesives were pre-heated to a glue pan temperature of 117 F. withreduced steam used on the first few double-backer hot plates. Thesurface temperature of the first hot plate was 290 F. The adhesive madefrom concentrate :4 was somewhat less expensive in addition to givingless trouble with foaming and having a somewhat better self-releasecharacteristic. While scraping was necessary on the hot plate, itrequired no real physical effort.

It has been determined that a truly self-releasing adhesive. that is, anadhesive which would pop off of the hot plate or be knocked loose by themovement of the liner board, must have a clean-up resistance no greaterthan 0.2 pound by our tests, preferably it should have a maximumresistance of 01 pound. We know of no so-called self-releasing silicateadhesive described in the prior art or used in practice which allows aclean-up resistance of as low as 0.1 pound on an uncoated or otherwiseuntreated hot plate surface. Truly self-releasing silicate adhesiveshave been obtained only with specially coated metal surfaces asdescribed above.

The term consisting essentially of" in the claims has been used todefine the essential novel ingredients of the adhesive composition, butsuch words are not intended to infer that one could not incorporate intothe claimed adhesive composition well known ancillary ingredients whichwould be obvious to those skilled in the art to which this inventionpertains. The term consisting essentially of in the claims has been usedto exclude components which would render the claims inoperative.

What is claimed is:

1. A novel adhesive composition having a low ad herence to metalconsisting essentially of:

(a) Aqueous sodium silicate,

(b) 0.25 to 2.0 wt. percent of an amyl ester of phosphoric acid, and

(c) At least one chemical compound selected from the group consisting ofurea, sugar, tiiethanolamine and a condensation product of rosin andmaleic anhydride and in the weight ranges of 1-592, 1-593, 0.1-2% and0.1-2% respectively.

2. A novel adhesive according to claim 1 wherein the amyl ester ofphosphoric acid is amyl acid phosphate.

3. A novel adhesive according to claim 1 wherein the amyl ester ofphosphoric acid is monodiamyl phosphate.

4. A novel adhesive according to claim 1 wherein the amyl ester ofphosphoric acid is monodi-iso-amyl acid orthophosphate.

5. A novel adhesive according to claim 1 wherein the amyl ester ofphosphoric acid is mono-iso-amyl acid orthophosphate.

6. A novel adhesive composition having a low adherence to metalconsisting essentially of:

(a) Aqueous sodium silicate,

(b) 0.25 to 2.0 wt. percent of an amyl ester of phosphoric acid, and

(c) Urea and triethanolamine in the weight ranges of 1-592 and 0.1-2%respectively.

7. A novel adhesive composition having a low adherence to metalconsisting essentially of:

(a) Aqueous sodium silicate,

(b) 0.25 to 2.0 wt. percent of an amyl ester of phosphoric acid, and

(c) 15% urea and 0.1-2% of a condensation product of rosin and maleicanhydride.

3,034,909 9 1O 8. A novel adhesive composition having a 10w ad-References Cited in the file of this patent herence to metal consistingessentially of:

. UNITED STATES PATENTS (a) Aqueous sodium silicate,

(b) 0.25 to 2.0 wt. percent of an arnyl ester of phos- 3 3 Fowler et g-1943 phoric acid,and 5 2,671,747 Lander Mar. 9, 1954 (0) 15% sugar and01-29; triethanolamine 2,736,678 Olix Feb. 28, 1956 9. A novel adhesivecomposition having a low ad- 2,772,996 Sams 1956 herence to metalconsisting essentially of; 2,788,285 Lander Apr. 9, 1957 (a) AQUEOUSsodium Silicate,

(b) 0.25 to 2.0 wt. percent of an amyl ester of phosphoric acid, andRalph W. Kerr: Chemistry and Industry of Starch (c) 1-5% sugar and(ll-2% of a condensation prod- Academic, 1950,13ag6 uct of rosin andmaleic anhydride.

1. A NOVEL ADHESIVE COMPOSITION HAVING A LOW ADHERENCE TO METALCONSISTING ESSENTIALLY OF: